Like mister23 said above, you can't remove yourself, the founding account is "undeletable", "unsubscribe-able" -> meaning the founding account cannot be removed.Instead, give your account (password) to the next admin in line, or a member of your choice. Inform them to change the password, email addresses in use, give them the URL of the utilities ( http://www.forumotion.com/en/utils/ ), give them the email address & password used there, inform them to change those details as well.

Vioala, now the forum should be handled by someone else and your no longer present.